This invention relates to a process for continuously conveying fine-grained or pulverized solid to two or several target points by means of a conveying medium. The solid is charged into a distribution vessel and, from there, the solid is conveyed to a selected one of a plurality of target points by means of the conveying medium moving the solid via one supply line each in the desired target flow rate. The invention also relates to apparatus for performance of the process.
The process of conveying fine-grained to pulverized solids by compressed air from a distribution vessel to several target points, and especially conveying of coal 10 dust to several consumers, such as tuyeres of a blast furnace, is known (DE-A 26 46 130, DE-C -30 50 394 and DE-A -25 37 370). In this process, especially close-grained flow conveying is applied. Coal dust is first pneumatically fed into a distribution vessel at the flow rate in which the coal dust is further delivered from this vessel. From the distribution vessel, several supply lines lead to the several target points, i.e., the tuyeres of the blast furnace. Each tuyere is charged with a material flow conveyed via a separate supply line.
It has turned out that the coal dust in the distribution vessel that acts as a static distributor is distributed to the individual supply lines with a relatively high accuracy (.+-.15% of the desired target flow rate). For instance, the target flow rate conveyed to the target points can be easily adjusted by adjusting the difference between the pressure at the target point and the pressure inside the distribution vessel.
Serious problems will occur if the target flow rate of the solid has to be adjusted or controlled individually for the target points commonly supplied by one distribution vessel. That requires installing control fittings, such as dampers, valves, etc., which allow flow rate adjustment, and mass flow meters in each supply line. However, insurmountable difficulties have been encountered in practice because such control fittings and mass flow meters are subject to extremely high wear from conveying fine-grained or pulverized solids. The failure of one control fitting will cause irregularities at the other target points. The replacement of a control fitting is expensive as conveying has to be interrupted.